Due to the low axial moment of inertia of such internal rotor motors, they are often used for drive applications, in which the movements of the electric motor must respond very rapidly to electrical commands, e.g. servo motors. In such a motor, the permanent magnets of the internal stator, which are arranged in a lamination stack associated with the internal rotor, cannot rattle or chatter, and must not, even at high rotation speeds, axially displace, i.e. they must be securely fixed, in the axial and radial directions, within the lamination stack. In the automotive industry, for example, in extreme installation contexts, it is required that the magnets must remain secure in the rotor, despite being subjected to an acceleration of 50 grams. With this objective, one can glue the permanent magnets in the lamination stack, or one can fasten, at both ends of the lamination stack, a securing disk which covers the magnets. One can also overmold the lamination stack with plastic, but all of these methods involve additional working steps, time, and supplemental materials. For gluing, special working stations with fume exhausting, etc. are necessary.
DE 10 2011 101 730 A1, and corresponding U.S. Pat. No. 8,569,922, ROMBACH, disclose an internal rotor motor, in which the permanent magnets are elastically clamped within the associated lamination stack. This is achieved by the fact that, using a tool, lugs arranged at the outer circumference of the lamination stack are pressed radially inward (indented, crimped). Thus, one obtains springy indented elements (indentations, crimpings) which each exert an radially inwardly directed force F in the direction of a respective pocket or recess, in which a permanent magnet of the internal rotor is placed, so that the magnet is clamped within the pocket.
A disadvantage is that these springy indented elements (indentations, crimpings), over the service life of the internal rotor motor, can rebound, allowing the permanent magnets to work loose, and thus rattle, or fall out of the pockets.
DE 10 2007 029 719 A, and corresponding WO 2008/092748-A, ROTH et al, disclose an internal rotor motor in which, at respective recesses of a lamination stack associated with the internal rotor, a resilient lug is provided which, in a load-free state resiliently engages in a corresponding recess. This resilient lug, upon insertion of a respective permanent magnet into the recess, is subjected to a force and thereby elastically deforms. Thus, after the insertion of the permanent magnet into the recess, the resilient lug exerts a respective force F against the permanent magnet, which keeps the magnet in the recess. It is nevertheless possible that, over the service life of the internal rotor motor, these resilient lugs may rebound, so that the permanent magnets, despite the use of these resilient lugs, can get loose and thus rattle, or fall out of the recesses.